1. Field of the Invention
This invention relates to an air conditioner for an automobile, or the like. More particularly, it is an air conditioner having a door which can be opened at a variable angle to produce an appropriate mixture of cold air and hot air having a desired temperature.
2. Description of the Prior Art
The prior art will be described with reference to FIGS. 4 to 6 of the accompanying drawings. Referring first to FIG. 4, there is generally shown an air conditioner which is installed in an automobile. It includes a number of doors which are provided for different purposes. An air intake door 12 is provided at the inlet of the air conditioner. It is movable between a first position at which it allows air to be drawn from the inside of the automobile into the air conditioner and a second position at which it allows air to be drawn from the outside of the automobile into the air conditioner. The air flowing into the air conditioner past the door 12 is directed by a fan motor 13 to an evaporator 14. The evaporator 14 cools the air and delivers cold air. Two air passages are provided downstream of the evaporator 14. The air leaving the evaporator 14 can flow into both of these air passages. The cold air leaving the evaporator 14 and flowing into one of the air passages remains cold when leaving the air passage. A heater 15 is provided in the other air passage for heating the cold air coming from the evaporator 14 and delivering hot air. The two passages meet at the outlets thereof to produce a mixture of the cold air and the hot air having an appropriate temperature. An air mixing door 11 is provided at the inlets of the two passages. It is movable between a first position at which it closes one of the air passages and a second position at which it closes the other passage. The door 11 is provided for varying the proportion by volume of the cold air flowing into one of the air passages and the cold air flowing into the other air passage. Therefore, the temperature of the air mixture obtained downstream of the two air passages depends on the proportion by volume of the cold air leaving one of the passages and the hot air leaving the other passage, i.e., the degree of opening of the door 11 relative to each passage. Three doors are provided at the outlet of the air conditioner. They are a door 17 which opens or closes a port leading to a vent, a door 18 which opens or closes a port connected to the floor of the automobile, and a door 19 which opens or closes a port leading to a window defroster. The doors 17 to 19 are selectively opened to enable the delivery of a stream of air having an appropriate temperature to the corresponding place or places.
The doors 12 and 17 to 19 are all simple in operation. They are all either totally open or totally closed. They are moved only for opening or closing the corresponding ports completely. On the other hand, the operation of the door 11 is complicated. The door 11 is not only movable between the two extreme positions thereof in which it opens one of the two air passages behind it completely, while closing the other passage completely. It is also required to take an intermediate position in which it is partly open with respect to both of the passages. Moreover, its angle of opening must be continuously variable with respect to both of the passages. As a natural consequence, a deliberately considered device is required for operating the door 11.
Referring now to FIG. 5, there is shown by way of example a conventionally available device for operating the door 11. It is a manual device. It comprises an L-shaped lever 20 and a wire 21 connected between the door 11 and the lever 20. The lever 20 is rotatable about a fixed pin 20b in either direction along an arrow line A--A in FIG. 5. The door 11 is rotatable about a pair of fixed pins 11a in either direction along an arrow line B--B. The lever 20 has one end 20c to which one end of the wire 21 is connected. The other end of the wire 21 is fastened to the door 11. The other end 20a of the lever 20 defines an actuator portion. If the actuator portion 20a is moved in either direction along the arrow line A--A, the lever 20 is rotated and its rotation is transmitted by the wire 21 to the door 11 so that the door 11 may be rotated along the arrow line B--B by an angle corresponding to the angle of rotation of the lever 20.
A large manual force is, however, required for moving the lever 20. This is particularly the case when the air conditioner is operating, since a high air pressure acts on the door 11. The manual movement of the lever 20 by overcoming the air pressure acting on the door 11 requires so large a force that the lever 20 is often difficult to move.
An electric device has, therefore, been proposed to overcome the drawback of the manual device as hereinabove described. It is constructed as shown by way of example in FIG. 6. It comprises a lever 1, an indicator panel 2, an electric motor 7, an actuator 8, a wire 10, a sliding potentiometer 22, a rotary potentiometer and a control box 24 as will hereinafter be described in further detail.
The panel 2 is provided with a temperature scale, etc. and has a slot in which the lever 1 is reciprocatively movable. The sliding potentiometer 22 is of the construction known in the art. It has a slidable member 22a to which the lever 1 is secured. It provides a certain amount of resistance which is determined by the position of its slidable member 22a, i.e., of the lever 1. It is connected to the control box 24 which contains a comparator, control circuit, etc. The motor 7 is connected to the control box 24 so that it may be rotated in either direction or stop its rotation in accordance with a signal from the control box 24. The motor 7 has an output shaft 7a to which one end of the actuator 8, which is in the form of a flat plate. is connected. The rotary potentiometer 23 has a rotative member 23a which is also connected to the output shaft 7a of the motor 7. The potentiometer 23 is of the type known in the art and is connected to the control box 24. It provides a certain amount of resistance which is determined by the angular position of its rotative member 23a, i.e., the angle of rotation of the output shaft 7a of the motor 7. The wire 10 has one end connected to the other end of the actuator 8 and the other end of the wire 10 is fastened to the door 11 to enable the rotation of the door 11 about a pair of fixed pins 11a.
The lever 1 is movable in either direction along an arrow line C--C in FIG. 6. If it is moved, the amount of resistance provided by the sliding potentiometer 22 is increased or decreased, depending on the direction in which the lever 1 has been moved. As a result, a difference appears between the amounts of resistance provided by the two potentiometers 22 and 23. This difference is detected by the comparator in the control box 24 and the control circuit transmits an appropriate signal to the motor 7 to cause it to rotate in either direction. If the motor 7 is rotated, the actuator 8 is rotated about the output shaft 7a of the motor 7 and the wire 10 is thereby moved to rotate the door 11 about the fixed pins 11a along the arrow line B--B. As the rotative member 23a of the rotary potentiometer 23 is also rotated, the amount of resistance provided by the potentiometer 23 is increased or decreased, depending on the direction of rotation of the output shaft 7a, and approaches the amount of resistance which is provided by the sliding potentiometer 22. It eventually coincides with the amount of resistance provided by the potentiometer 22. This coincidence is detected by the comparator and the control circuit in the control box 24 outputs a signal to the motor 7 to stop its rotation.
The electric device has a number of advantages. The lever 1 is easy to move by the motor 7, even if a high air pressure may act on the door 11. The device enables fine control of the temperature of the air leaving the air conditioner, as the comparator, etc. in the control box 24 make it possible to control the angular position of the door 11 precisely in accordance with the amount of sliding movement of the lever 1.
The device has, however, a number of drawbacks, too. The control box 24 is expensive and adds greatly to the cost of the device as a whole. Moreover, a serious problem occurs if the control box 24 receives a noise signal. The noise causes the comparator to work erroneously and thereby disables the angular position of the door 11 to be controlled accurately in accordance with the amount of movement of the lever 1.